The present disclosure generally relates to a furnace flue gas connection that adjusts to movement caused by expansion.
Various furnaces are used in industry to create power, incinerate waste or perform chemical processes. The flue gases are conveyed by interconnected flue gas ducts. These must maintain a gas-tight seal to prevent leakage of flue gases.
FIG. 1 shows flue gas ducts 1 from a conventional furnace 3 (partially shown). The flue gas ducts 1 include a top pass 7 starting above a nose 5 of the furnace 3 connecting to a backpass 9.
The backpass 9 extends downward to an economizer gas outlet duct 11. A backpass outlet manifold 12 attached to the economizer gas outlet duct 11. The backpass outlet manifold 12 includes an ash hopper 45 adapted to collect fly ash carried by the flue gases.
Support structures 37 extend over the furnace and flue gas ducts 1. The furnace 3 and flue gas ducts 1 typically are hung from the support structures 37 with hanger rods 39. The furnace 3 is typically fixed at its top left. When the backpass 9 and the flue gas ducts 1 expand, they move downward as shown by arrow “A” and to the right, as indicated by arrow “B”.
An air preheater duct 10 extends vertically from the air preheater (not shown) that is secured to a floor. When air preheater duct 10 heats up, it expands upward in the direction shown by arrow “C”. An elbow duct 19 is attached to the air preheater duct 10, which also moves upward as air preheater duct 10 expands. The motion due to thermal expansion causes the backpass outlet manifold 12 to become misaligned with the elbow duct 19.
Therefore a toggle section 13 is typically employed to adjust for the misalignment and movement due to thermal expansion. The toggle section 13 is designed to make a gas tight connection between the backpass outlet manifold 12 and the elbow duct 19. Since the expansions cause motion in the three directions indicated by arrows “A”, “B” and “C”, there should be some flexibility built into the toggle section 13.
Toggle section 13 includes expansion joints 15 on either side of a toggle duct 17. These are designed to adjust to the various movements of the ducts.
With the increase in size and power of furnaces and boilers, there is increased expansion requiring the toggle section 13 employed to become larger and heavier. These larger toggle sections 13 require additional support structures and make the system more expensive.
Reheater vertical tubes 41 support the reheaters 29 and economizer vertical tubes 43 support the economizers 33 in the backpass 9.
The fly ash and hopper 45 add considerable weight that must supported by the vertical tubes 41, 43, support structures 37 and hanger rods 39.
Since the toggle sections are getting larger with larger boilers, they require extra room, which results in a larger ‘footprint’. This larger footprint also incurs increased costs.
Currently, there need for a device to provide a lighter, smaller, simpler, and less expensive gas-tight connection to connect misaligned flue gas ducts.